Evolution of New Genotype of WNV in North America | CDC EID

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Volume 17, Number 5–May 2011
Research
Evolution of New Genotype of West Nile Virus in North America
Allison R. McMullen, Fiona J. May, Li Li, Hilda Guzman, Rudy Bueno, Jr., James A. Dennett, Robert B. Tesh, and Alan D.T. Barrett

Author affiliations: University of Texas Medical Branch, Galveston, Texas, USA (A.R. McMullen, F.J. May, L. Li, H. Guzman, R.B. Tesh, A.D.T. Barrett); and Harris County Public Health and Environmental Services, Houston, Texas, USA (R. Bueno, Jr., J.A. Dennett)

Suggested citation for this article


Abstract
Previous studies of North American isolates of West Nile virus (WNV) during 1999–2005 suggested that the virus had reached genetic homeostasis in North America. However, genomic sequencing of WNV isolates from Harris County, Texas, during 2002–2009 suggests that this is not the case. Three new genetic groups have been identified in Texas since 2005. Spread of the southwestern US genotype (SW/WN03) from the Arizona/Colorado/northern Mexico region to California, Illinois, New Mexico, New York, North Dakota, and the Texas Gulf Coast demonstrates continued evolution of WNV. Thus, WNV continues to evolve in North America, as demonstrated by selection of this new genotype. Continued surveillance of the virus is essential as it continues to evolve in the New World.


West Nile virus (WNV) is a mosquito-borne flavivirus belonging to the Japanese encephalitis serogroup and maintained in an enzootic cycle between mosquitoes (primarily Culex spp.) and birds. Mammals such as horses and humans act as dead-end hosts. Most human infections are asymptomatic; West Nile fever develops in »20% of infected patients and neuroinvasive disease develops in <1% (1). WNV was first isolated in Uganda in 1937 and was generally associated with sporadic outbreaks of mild, febrile illness until the 1990s, when several epidemics of neuroinvasive disease were reported in northern Africa, eastern Europe, and Russia (2–4). In 1999, WNV was first isolated in North America from human and bird samples during an outbreak of encephalitic disease in New York. After this outbreak, WNV rapidly spread across the United States north to Canada and south to the Caribbean region, Mexico, and Central and South America. By 2002, the original WNV genotype isolated in New York, known as NY99, was displaced by a new genotype, designated the North American (NA) or WN02 genotype (hereafter termed NA/WN02 genotype) (5,6). This genotype is characterized by 13 conserved nt changes, 1 of which results in an amino acid substitution, V159A, in the envelope (E) protein. The NA/WN02 genotype is believed to have become dominant in North America because of its ability to more efficiently disseminate in mosquitoes than the original NY99 virus genotype (6–8). Beasley et al. (9) first identified the NA/WN02 genotype in Texas in 2002, and further studies showed that this genotype had spread throughout the Upper Texas Gulf Coast and to other regions in the United States (5). Additional studies examined phenotypic changes in WNV isolates from the Upper Texas Gulf Coast region during 2003 and identified co-circulation of small-plaque, temperature-sensitive, mouse-attenuated and large-plaque, non–temperature-sensitive, mouse-virulent strains (10–12). Subsequent studies of the E gene of viruses isolated through 2006 suggested that since the emergence of the NA/WN02 genotype, WNV in North America is either genetically homeostatic (13) or its growth rate is decreasing (14). We examined genetic variation in selected WNV strains since 2005 from the Upper Texas Gulf Coast region, in particular, Harris County, Texas, USA (Houston metropolitan area). We report the isolation of genetic variants that demonstrate the continuing evolution of WNV in North America. We also show that the southwestern US genotype first identified in Arizona, Colorado, and northern Mexico in 2003 (termed SW/WN03 genotype) has now spread to the Upper Texas Gulf Coast region. full-text: Evolution of New Genotype of WNV in North America | CDC EID


Suggested Citation for this Article
McMullen AR, May FJ, Li L, Guzman H, Bueno R Jr, Dennett JA, et al. Evolution of new genotype of West Nile virus in North America. Emerg Infect Dis [serial on the Internet]. 2011 May [date cited].
http://www.cdc.gov/EID/content/17/5/785.htm

DOI: 10.3201/eid1705.101707


Comments to the Authors
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Alan D.T. Barrett, Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555-0609, USA; email: abarrett@utmb.edu